1. Field of the Invention
This invention relates to an actuator movable by the energy of fluid, and more particularly to an actuator which can be reduced in diameter and can take a smooth motion at a multi-degree freedom.
2. Description of the Prior Art
Heretofore, it has been a common practice to use a hydraulic or pneumatic cylinder, a hydraulic or pneumatic motor, etc. as an actuator movable by the energy of fluid.
This conventional actuator generally has a sliding contact (e.g., between a piston and a cylinder) so that an operating fluid can easily leak out. Because of the sliding friction, smooth motions and precise positioning are difficult to achieve.
To this end, a pneumatic actuator utilizing the elastic deformation of rubber has been proposed. This prior art is exemplified by a Pneumatic Finger (trade name), German Pt. No. 2,426,086-C3 and U.S. Pat. No. 3,981,528.
As shown in FIGS. 1 and 2 of the accompanying drawings, this prior actuator comprises an elastic body 301 in the form of a rubber tube having a semicircular cross section, the elastic body 301 being provided axially partially with bellows 303c. The elastic body 301 has at one end a port 305 through which air is to be forced. Consequently when the pressure in the elastic body 301 is increased by supplying an air pressure P into the elastic body 301 from the port 305, the bellows 303 are forcibly expanded to cause the entire elastic body 301 to elastically deform to take a bending action, as indicated in phantom lines 301b in FIG. 1. At that time, by adjusting the pressure in the elastic body 301, it is possible to control a potential A, V (functions of position) of a distal end of the bent elastic body 301 and a force F acting on that distal end, as shown FIG. 1. Thus this prior actuator can take smooth motions without any leak of the acting fluid like the conventional cylinder.
However, when this known actuator is merely used to construct a slender small-sized robot arm, the bellows occupies a certain extent of space in order to take a multi-degree freedom into practice. Therefore it is possible to reduce the diameter of a robot arm by only a limited extent.
Thus the actuator utilizing the deformation of an elastic body with belows can move smoothly without any leak of the acting fluid like a cylinder. But since provision of bellows necessitate a large diameter tube, this type of actuator is not suitable for a multi-degree-freedom robot arm.
Further, when a rotating motion about the axis is to be added to the above robot arm, the actuator must be combined with a different-type actuator, with the result that the entire actuator would be more complex and hence expensive, thus making it also difficult to achieve a reduced diameter.